Although the use of dual pole solenoids appears to dominate in most fuel injector solenoid applications, single pole solenoids still remain preferred in some applications. In most dual pole solenoid designs, an armature is spaced at an axial air gap distance away from a stator having a coil embedded therein. Dual pole solenoids are often identified by an armature diameter that is typically about the same or greater than the outer diameter of the coil winding of the stator assembly. When the coil is energized, magnetic flux is generated around the coil, and flux lines pass through the stator, to the armature and back to the stator. The resulting flux path produces a pair of magnetic north and south poles between the stator and armature on each side of the air gap. The flux between these poles is generally parallel to the armature motion. These opposite poles produce a force on the armature that tend to move it in the direction of the stator and coil to accomplish some task, such as to open or close a valve, etc. In the case of all solenoids, a magnetic flux path is created around the coil.
In a typical single pole solenoid, the magnetic flux path also encircles the coil and passes through the stator, the armature, and back to the stator. The resulting flux path also produces a pair of magnetic north and south between the stator and the armature. In the single pole configuration, the flux between the poles is parallel to armature motion for one set of poles and perpendicular to armature motion for the other set of poles. Only one set of poles is producing magnetic force for armature motion. In both single and dual pole designs, the armature generally moves toward the stator to reduce the size of the air gap their between.
In many single pole solenoid designs, the armature must also have a radial sliding gap with respect to another electro magnetic component that is present to complete the magnetic circuitry. Single pole solenoids are often identified by an armature diameter that is smaller than the inner diameter of the coil winding of the stator assembly. Due primarily to manufacturing considerations, this extra magnetic piece is often not included as a portion of the stator, but is generally in contact with the stator, stationary and positioned to complete the magnetic circuit of the solenoid. Depending upon the configuration of the single pole solenoid, this additional magnetic component is sometimes referred to as a magnetic flux ring. When the coil is energized, the magnetic flux lines encircle the coil and pass sequentially through the stator, the magnetic flux ring, the armature, and back to the stator, or vice versa. Since the magnetic flux ring is stationary but the armature moves, there must be a sliding air gap between these two components. However, those skilled in the art will appreciate that this sliding gap is preferably as small as possible in order to produce the highest possible forces on the armature. When this sliding air gap becomes so small that the armature touches the magnetic flux ring, a high magnetic force is produced but the armature may be unable to move. When the sliding gap becomes too large, the magnetic flux can sometimes tend to seek out a lower reluctance path than spanning the sliding gap such that the solenoid can begin to perform poorly.
Typically, the armature may be guided by an armature guide piece, which is guided via an interaction with a guide bore. Those skilled in the art may recognize parallelism issues that may be related to guiding an armature guide piece via a guide bore. For instance, the guide piece might be a valve member that is attached to the armature, causing the sliding air gap geometry of the solenoid assembly to be dictated by the guiding interaction of the valve member, which is not really a part of the solenoid assembly. One potential problem with these configurations includes misaligning the armature guide relative to the guide bore, thereby causing the armature guide piece to contact the guide bore on one side, adversely affecting the movement of the armature guide piece inside a single pole solenoid assembly. The misalignment may further result in the armature leaning towards one side thereby contacting the flux ring component on one side while moving a distance away from the other side, potentially causing scuffing and an asymmetry in the magnetic flux, hence adversely affecting performance. Furthermore, excessive contact between the armature and the flux ring component may damage the armature, which is also undesirable.
The prior art teaches the use of a flux ring component to reduce the size of the sliding radial air gap to increase solenoid force. Co-owned U.S. Pat. No. 6,279,843 to Coldren et al. appreciates the importance of maintaining small axial and sliding radial air gaps, but fails to address the issues stemming from an armature guide piece guiding the armature via an interaction with a guide bore. Although the '843 patent teaches reducing misalignment by concentrically coupling the centerlines of the armature and the magnetic flux ring component, it still can suffer misalignment and performance problems due to geometric tolerance stack ups that must inherently be part of a multi-component assembly.
The present disclosure is directed toward at least one of the problems set forth above.